1. Field of the Invention
The present invention relates to a conveyance system for conveying one or more wafers between a plurality of wafer processing apparatus.
2. Description of the Related Art
The manufacture of integrated circuits (IC's) and Large-Scale Integration (LSI) logic onto wafer substrates may require large amounts of processing to be performed on the wafers. Wafers may need to be conveyed to a variety of processing apparatuses during the manufacturing process. FIG. 1 is a schematic plan view showing equipment for processing wafers. The equipment may sequentially perform processes A-Z on the wafers. Wafer processing apparatus A, wafer processing apparatus B, etc. through wafer processing apparatus Z may be arranged as shown. These wafer processing apparatuses may be provided with stockers SA, SB, etc. through SZ for each processing apparatus. Each stocker may house a plurality of cassettes capable of accommodating stacked wafers. Additionally, n wafer processing apparatuses A1-An may be arranged in a row. And n wafer processing apparatuses B through Z may be arranged as the n wafer processing apparatus A1-An. A rail AR, BR, etc. through ZR from the stocker corresponding to each wafer processing apparatus may be provided adjacent the n aligned wafer processing apparatuses. The rail AR, BR, etc. through ZR may be arranged for guiding a cassette transfer apparatus (not shown) to convey cassettes from one apparatus to another.
A cassette transfer apparatus traveling along the rail AR may withdraw a cassette from the stocker SA, move the cassette along the rail AR, and place the cassette in front of the wafer processing apparatus A1. Referring also to FIG. 2, when the cassette transfer operation has been performed, a cassette 4 housing a plurality of stacked wafers may be positioned in front of n wafer processing apparatus A. A wafer transfer apparatus 2 may be arranged between the cassette 4 and the wafer processing apparatus A. The wafer transfer apparatus 2 may remove a wafer in the cassette 4 and set it in the wafer processing apparatus A. After the set wafer has undergone the process A by the wafer processing apparatus A, the A-processed wafer may be extracted from the wafer processing apparatus A by the wafer transfer apparatus 2 and re-housed in the cassette 4. When this process has been performed for every wafer in cassette 4, the wafers may be returned to the stocker SA by way of the in-process cassette transfer apparatus which may travel along the rail AR.
The cassette 4 which now includes wafers that have undergone the process A may be moved from the stocker SA to the stocker SB, which may correspond to the wafer processing apparatus B. The movement of the cassette 4 between stockers may be performed by means of an inter-process cassette transfer apparatus (not shown). The inter-process cassette transfer apparatus may move on the rail SR provided parallel to each stocker. This inter-process cassette transfer apparatus may remove the cassette 4 from the stocker corresponding to the wafer processing apparatus of the previous stage, move to the position in front of a stocker corresponding to the wafer processing apparatus of the next step, and place the cassette 4 in this stocker. In this way, the cassette 4 may be moved between stockers.
When the cassette 4 is moved from the stocker SA to the stocker SB by the inter-process cassette transfer apparatus, the cassette 4 may be conveyed from the stocker SB by the in-process cassette transfer apparatus along the rail BR. The wafer transfer apparatus provided for each wafer processing apparatus B may remove one wafer at a time from the cassette 4 as in the case of the process A described above. The wafer transfer apparatus may set the wafer in the wafer processing apparatus B to perform the process B. After the processing, the B-processed wafers may be returned to the cassette 4, and when all of the B-processed wafers have been returned to the cassette 4, the cassette 4 may be returned to the stocker SB by the in-process cassette transfer apparatus. LSI and IC's may be produced by repeating this type of operation through process Z.
Using the semiconductor producing equipment described above, it is not possible to go on to process B until process A has been completed with respect to all of the wafers housed in the cassette 4 housed in the stocker. A large amount of time may occur to produce semiconductors which necessitate a large number of processing steps. Additionally, during the period from when the process A has been performed until the next process B is performed, the processed wafers may be housed for a long time inside cassette 4. If the wafers are left for a long time after performing a wafer cleansing process before going on to the next coating process, dust may adhere to the wafers or the wafers may oxidize, thus reducing the yield.
Although production time may not be a problem when performing mass production of the same type of product, in the case of small-scale production of a prototype or other small-scale projects, a large production time may be a problem. Since a large number of transfer apparatus, such as an in-process cassette transfer apparatus, inter-process cassette transfer apparatus and wafer transfer apparatus are required, the cost of equipment production may increase, thereby increasing the production cost of the final product.